1. Field of the Invention
The present invention relates to a glass-ceramic composite material.
2. Description of Related Art
Glass-ceramic composite materials have been known, and especially those including a glass matrix and filler particles dispersedly disposed in the glass matrix are identified as suitable for Low Temperature Co-fired Ceramics (LTCC).
In particular, as the materials favorably used for substrates with internally formed wiring sections formed by metal (such as gold or copper), which is of low electric resistance, a multitude of glass-ceramic composite materials including aluminum nitride particles employed as the above-described filler particles have been suggested (refer to, for example, JP H02-221162 A, JP H04-254477 A, JP H06-16477 A, JP 2001-342063 A, JP 2002-348172 A, JP 2003-73162 A, JP 2003-137657 A, JP 2005-533744 A).
However, the glass-ceramic composite materials using the aluminum nitride particles as the filler particles as described above have been commonly found in patent documents, but have not been in practical use yet. After elaborate study, the applicant (inventors) of this application has discovered that there is great variability in a formation state (thickness) of an oxide film formed on a surface layer of the filler particle, resulting in the presence of a region where wettability to the glass matrix is low on the surface of the filler particle. This is a reason why the glass-ceramic composite materials have not been developed for the practical use.
More specifically, when the oxide films are formed on the surface layers (the surfaces) of the filler particles formed by the aluminum nitride particles, wettability to the glass matrix is generally improved, to thereby increase a thermal conductivity. In this regard, aluminum nitride particles have angulated shapes in materials of the above-described type according to a related art. Because of the angulated shape, corner portions are preferentially oxidized, while a planar portion between corner portions undergoes oxidization at a lower rate of progress and accordingly remains low in wettability to the class matrix. Thus, in such a state under the presence of great variability in formation state of the oxide films on the surfaces of the filler particles, sintering performance is deteriorated, and the thermal conductivity is also decreased.
Here, as a certain qualified approach for improving wettability to the glass matrix, it is at least conceivable that the thickness of the oxide film is wholly increased to form the sufficiently thick oxide film even on the planar portion between the corner portions. In this approach, however, a proportion of an aluminum oxide having a low thermal conductivity is increased in the filler particle, which instead results in a decreased thermal conductivity of the glass-ceramic composite material as a whole.